Same as the .500 WE case? It has the belt to head space on. As far as the internet shows, it is considered a straight walled case. Some .50 subs use a belted case, but maybe only for the needed body diameter. Head space made possible with the belt, having no shoulder.

Interesting question, never thought about it. Straight wall case has meant a rimmed cartridge to me. The .458x2, .458 Winchester, and .458 Lott, are pretty much what you're talking about, and are commonly referred to as "belted magnums". However, cartridge nomenclature doesn't have a lot of hard fast rules. If you want the belt to be just a different rim style it works. If you come up with something new call it what you want.